F5 Chem!!! 急問!! 15 marks!! chem高手請進!!!!!!!!!!!!!!urgent

2008-04-28 2:36 am

==>2002 A black powder is suspected to be carbon or a mixture of carbon and
copper(II) oxide. Which of the following methods can be used to identify
the black powder ?
(1) adding dilute sulphuric acid to the powder
(2) adding sodium hydroxide solution to the powder
(3) heating the powder strongly
A. (1) only
B. (2) only
C. (1) and (3) only
D. (2) and (3) only
Ans is C, WHY?

==>which powder needs the shortest time to react with dilute sulphuric acid completely?
A. 7g of Calcium
B. 8g of magnesium
C. 8g of zinc
D. 4g of copper

2007 Q40 paper 2 / 2005 Q39 Paper 2 / 1992 paper 2 Q27
可唔可以explain點解個ans會係咁...

仲有,NaCl+ chlorine water有冇reaction ga?

唔該快d解答!!好urgent

更新1:

which powder needs the shortest time 果題的ans係b, but why?

更新2:

RE:LoveJoe 點解第二題no. of moles最多,時間就最快????

回答 (2)

用戶7369

2008-04-28 2:55 am

✔ 最佳答案

1. copper ii oxide will dissolve in sulphuric acid to
form blue copper ii sulphate solution.
2. although calcium is more reactive than magnesium,
calcium will form a insoluble layer (calcium sulphate)on
the surface of calcium . so the rate of reaction is lowered.
so magnesium is the answer.
3. Cl2 + H2O <------> HCl + HOCl
when concentrated sodium chloride is added ,
the equilibrium position will shift to the left.
so pale yellowish green colour of chlorine gas will come out.

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hiuyi

2008-04-28 2:48 am

我想答你個兩題mc
第一題
1) dilute sulphuric acid 只會同CuO有反應變成藍色既solution，而cu係唔會同佢有反應，因為佢既reactivity太低
2)兩個都會冇反應，因為cuo要同NH3先有反應
3)heating會令cuo變返reddish brown既cu，所以可以分到

第二題
要計下邊個既no. of moles係最多，可能仲要諗下佢地既reactivity，而cu係冇反應既...

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